1. Technical Field
The present disclosure relates to an image forming apparatus such as a copier, a printer, a facsimile machine, or a combined machine thereof. The present disclosure also related to an image forming method.
2. Description of Related Art
In an electrophotographic image forming apparatus, a surface of a photoreceptor, serving as a latent image bearing member, is charged by a charger and the charged surface is exposed to light emitted from an exposure device so that an electrostatic latent image is formed thereon. The electrostatic latent image is then supplied with toner, serving as a developer, from a developing device and developed into a toner image. The toner image on the photoreceptor is transferred onto a sheet of paper, serving as a recording medium, by a transfer device. Alternatively, the toner image on the photoreceptor is first transferred onto an intermediate transfer belt, serving as an intermediate transfer medium, and then transferred onto the sheet of paper from the intermediate transfer belt.
A typical transfer device has a transfer roller that serves as an electrode. The transfer roller is supplied with a voltage having the opposite polarity to the toner to form a transfer electric field between the transfer roller and the photoreceptor. When the toner image on the photoreceptor reaches a transfer position where the photoreceptor faces the transfer roller as the photoreceptor rotates, the toner image is transferred from the photoreceptor onto the sheet of paper or intermediate transfer belt by the electrostatic force generated in the transfer electric field.
At the same time, the surface of the photoreceptor passes through the transfer position while being effected by the charge of the transfer roller. As a result, the surface of the photoreceptor is charged to have the opposite polarity to the toner. Thus, the difference in potential between the developing device and the photoreceptor is lowered and the amount of toner supplied from the developing device to the photoreceptor is unnecessarily increased, causing a problem such that the back surface of the sheet of paper is contaminated with the toner. In attempting to solve this problem, JP-3457083-B2 (corresponding to JP-H08-234646-A) proposes a neutralizer that neutralizes the surface of the photoreceptor after the surface has passed through the transfer position.
However, installation of the neutralizer undesirably makes the apparatus much larger in size and cost.